Errors in the birthing process can take place in many ways. One of them is improper cervical dilatation. There can be excessive dilation or the lack of dilatation. If excessive; premature labor can occur. If ordinary dilatation is lacking; obstructive labor takes place causing fetal anoxia or worse. Either way cervical elasticity is an important quantity to be measured and controlled in any attempt to manipulate labor. As a means to control this important physiological quantity, we are studying the stress-strain characteristics of the rabbit cervix. We will use it as a model of the human cervix. In addition, we are attempting to control the elasticity of the cervix by the in vitro addition of the prostaglandins PGE2 PGF2 alpha, PGE1, PGF 2 alpha 16,16 dimethyl ester, urea and indomethacin. We hope to use the non-pregnant and pregnant rabbit as a model in the pursuit of chemical agents that can be used to control human cervical elasticity. Strips of the cervix will be stretched and the stress-strain curves evaluated by linear regression analysis to obtain a single parameter, the stretch modulus, and this will be used to compare the various drugs and treatments.